Long Term Evolution (LTE) is the fourth-generation (4G) wireless communication technologies standard developed within the 3rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunication System (UMTS) standard. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) is the RAN of an LTE system. In an E-UTRAN, a User Equipment (UE) is wirelessly connected to a Base Station (BS) commonly referred to as an evolved NodeB (eNodeB or eNB) in LTE. A BS is a general term for a network node capable of transmitting radio signals to a wireless device and receiving signals transmitted by the wireless device.
System Architecture Evolution (SAE) is the core network architecture of 3GPP's LTE wireless communication standard. The SAE has a flat, all-Internet Protocol (IP) architecture with separation of control plane and user plane/data traffic. The main component of the SAE architecture is the Evolved Packet Core (EPC), also known as SAE Core. Some important subcomponents of the EPC are Mobility Management Entity (MME) which is the key control node for the LTE access-network, Serving Gateway (SGW) which routes and forwards user data packets, Packet data network Gateway (PGW) providing connectivity from the UE to external packet data networks by being the point of exit and entry of traffic for the UE and acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies, and Home Subscriber Server (HSS) which is a central database that contains user-related and subscription-related information.
A communications network, which may be a wireless communication network, can be viewed in many ways. One way is a deployment view, where deployment refers to the physical placement of network equipment. Equipment is placed at sites. FIG. 1a shows such sites and how they may be connected.
End user devices are not illustrated in FIG. 1a. However, a device may be connected to the network, e.g., via a base station illustrated by an antenna icon, via a small cell and distributed radio (DR), or via a fixed line or a WiFi link illustrated in the FIG. 1a by a house icon or an office icon. Traffic is carried through an aggregation network, where Ac in the FIG. 1a is used for access sites and Ag is used for aggregation sites. Access and aggregations sites are often called hub sites or central office sites. Further aggregation may be done through a backbone network (BB) towards centralized data centers (DC). Some of these data centers may also act as a primary site (P). Some data centers, illustrated as the globe icons in FIG. 1a, may also do peering towards external Internet. Note that site naming is not standardized and may differ between operators. The naming above is just one example.
The deployment may be visualized in another way, illustrated in FIG. 1b. Different network services are mapped to different sites in this view. The services are here the network nodes of the 3GPP Evolved Packet Core (EPC) architecture as defined in the 3GPP standard (TS 23.401). Local sites may host antennas and eNBs. Regional sites are mainly used for aggregation. National sites host core network nodes like MME, SGW, PGW and Policy and Charging Control Function (PCRF). Some national sites may act as primary sites hosting user subscription information in a HSS.
To give an example, a large operator with more than 100 million subscribers spanning a large country may have 50000 BS sites, 150 central office sites, 25 regional data centers and 5 national data centers where each national data center also does peering towards external Internet. A BS site spans a couple of thousands of end users in a city district, a central office site spans a larger city, a regional data center spans a few million users in a part of a large state or in a number of small states, and a national data center spans tens of millions of users in a complete region of the country.
The current 3GPP EPC architecture is an anchored architecture. This means that all traffic of an Access Point Name (APN) of a user device needs to pass through one and the same PGW. With such architecture and a deployment as described above, it will be clear that the traffic in the network will follow a topological tree structure. The leaves of the tree are the end devices, the branches are the local and regional sites, and the trunk is the national data center hosting the PGW. Traffic from one end device to another end device will have to pass at least one, sometimes even two, PGWs. This also means that there may be a large latency in the transport of the packets, even if the two end devices are physically close to each other. The PGW may be hosted in a national data center physically far from the end devices. This applies also when one of the devices is located in another network, e.g. a server on the Internet.
IP networks use address aggregation to achieve routing scalability. This results in IP addresses having location significance in the network. That is, when a device with an IP address moves, it is not easy to reflect the change of the location of its IP address in the routing system. This is usually solved by allocating a fixed-location anchor point to the device managing its IP address. The anchor would then tunnel the traffic incoming to the device to the current location of the device. Mobile IP or General Packet Radio Service (GPRS) Tunneling Protocol (GTP) are protocols doing this. In the following, the place in the network topology where the IP address of the device is advertised is called an IP Advertisement Point (IAP). In today's mobile and fixed networks the IAP of the end user device, sometimes referred to as the UE, is typically anchored in a node as already mentioned above. In an anchored architecture, the IAP acts as anchor and is located in e.g. the PGW or a Broadband Network Gateway (BNG) for as long as the UE is using that IP address. The UE may e.g. use the IP address until the UE detaches or the IP address is released or re-assigned e.g. using Dynamic Host Configuration Protocol (DHCP).
All incoming traffic to the UE needs to go through the IAP, meaning the placement of the IAP in relation to the UE and its communication peer will determine how optimal the packet routing will be towards the UE. I.e. if the IAP is placed close to the UE, traffic from different sources can take a fairly optimal route to the IAP and the UE, if the IAP is far away from the UE, e.g. located on some core site, the traffic routing will often be less optimal. The drawback though of placing the IAP more distributed, i.e. closer to the UE, appears when the devices such as a wireless UE moves in the network. At that time the routing, although initially optimal, could become sub-optimal after some UE mobility. This is illustrated in the FIGS. 2a-d. In FIG. 2a, the IAP is placed in a central location. Routing of IP flow 1 is optimal but routing of IP flow 2 is sub-optimal. In FIG. 2b, the IAP is placed in a distributed location, leading to more efficient routing for both flows in the static case, i.e. when the UE is not moving. However, in FIG. 2c the IAP is also placed in a distributed location, leading to less efficient routing for both flows in the case of a mobile UE, and in FIG. 2d, the IAP is again placed in a central location, which in the mobility case leads to a more efficient routing for both flows in this example.
FIGS. 2a-2d thus illustrates how the placement of the anchor point or the IAP can support optimized routing. Moving an anchor is not possible. However, multiple IAPs may announce the same IP address. In such anchorless setup, optimized routing can be achieved by using that IAP that is on the optimal routing path. There may be one or more functions for processing data packets of a flow associated with a device or UE which are on the routing path UE-IAP-peer. If the data packets of the flow after movement of the UE start to go through a different path, and possibly via a different IAP, then those functions may still be on a sub-optimal routing path. Hereinafter, the term functions for processing data packets is equivalent to the term packet processing functions. Examples of packet processing functions are firewall, Network Address Translation (NAT), charging functions, policy functions, and lawful interception function.